Component Events: Way to Communicate Between Components in Containment Hierarchy

SK_ChildCmp.cmp

<aura:component >
    <aura:attribute name="childValue" type="string" default="Child"/>
    <aura:registerEvent name="changeValueEvent" type="c:SK_LightningEventChannel"/>
    <lightning:button name="ddff" label="Fire event" onclick="{!c.fireEvent}"/>
</aura:component>

SK_ChildCmpController.js

({
	fireEvent : function(component, event, helper) {
		console.log('********firing event');
        var newEvent = component.getEvent("changeValueEvent"); 
        newEvent.setParams({"passedValue":"twitter handle-@sunil02kumar"});                               
        newEvent.fire(); 
	}
})

SK_ComponentEventPracticeApp.app

<aura:application extends="force:slds">
    <c:SK_MasterCmp/>
</aura:application>

SK_LightningEventChannel.evt

<aura:event type="COMPONENT" description="Event template" >
    <aura:attribute name="passedValue" type="string"/>
</aura:event>

SK_MasterCmp.cmp

<aura:component >
    <!--name should be equal to name while register event-->
    <aura:handler name="changeValueEvent" event="c:SK_LightningEventChannel" 
                  action="{!c.handleNotification}"/>
    <aura:attribute name="mastervalue" type="string" default=""/>
    <div style="background-color:#E6E6FA;border-style: solid;height:200px;margin:5%;padding:2%;">
    	<p>This is master Component- container for c:SK_ChildCmp</p>
        <br/>
        Display  value passed from child component using component events---<b>{!v.mastervalue}</b>
    	<br/>
        <div style="background-color:grey;border-style: solid;padding:2%;">
            <p>This is child component present inside c:MasterCmp</p>
            <c:SK_ChildCmp/>
        </div>
        
    </div>
	
</aura:component>

SK_MasterCmpController.js

({
	handleNotification : function(component, event, helper){
        console.log('****handling event');
        var sentMessage= event.getParam("passedValue");
        component.set("v.mastervalue", sentMessage);
    }
})